1. Field of the Invention
The present invention relates to an apparatus for feeding a packing material along a filling tube of a vertical-type bag form-fill-sealing machine.
2. Description of the Related Art
A packing material feeding apparatus of the type mentioned above feeds a packing material surrounding the outside of a filling tube along the filling tube at a constant velocity during a normal, operation of a vertical-type bag form-fill-sealing machine, where both side edges of the packing material are overlapped in a predetermined form.
While the packing material is being fed, both side edges of the packing material are thermally sealed in sequence to form a center seal on the packing material. This center seal forms the packing material in a completely cylindrical shape.
Then, the cylindrical packing material is again thermally sealed every predetermined feeding length to form a top seal on the packing material. Immediately after the formation of the top seal, the packing material is cut from the center of the top seal. As a result, bags each having a predetermined length are periodically formed from the packing material.
On the other hand, a measuring device of the machine periodically fills articles into the packing material through the filling tube. The filling of articles is performed alternately with the formation of the top seal. As a result, bags periodically formed from the packing material can individually receive the supplied articles and hence accommodate the articles therein.
As will be understood from the foregoing, it should be ensured that the articles are filled in the packing material within a period required to form one bag, i.e., within a unit packing period. However, the operation involved in filling the articles from the measuring device is susceptible to temporary instability due to certain states of the articles accumulated in the measuring device, more specifically, due to an increased and decreased amount of accumulated articles, partial accumulation, and so on, resulting in a situation where the articles are not filled in a bag within the unit packing period, i.e., xe2x80x9cnon-fillingxe2x80x9d of articles.
If the packing material was continuously fed and formed with a top seal and cut in association with the feeding during such article non-filling state, the machine would produce empty bags which accommodate no articles. To avoid producing such empty bags, the operation of the machine must be shut down, that is, the packing material must be prevented from being fed immediately at the time the xe2x80x9cnon-fillingxe2x80x9d of articles occurs. Such shut-down would result in a significant reduction in productivity.
An example of a packing machine intended to eliminate the foregoing defect is disclosed, for example, in Japanese Patent Publication No. Hei 7-67925. In this known packing machine, when the xe2x80x9cnon-fillingxe2x80x9d of articles occurs, the packing material is fed at a lower velocity. Subsequently, as the packing machine resumes filling articles, the lower velocity in feeding the packing material is immediately released to increase the packing material feeding velocity to a normal velocity, followed by a normal operation of the packing machine. In this way, the packing material feeding control as described above reduces the number of times the packing machine is shut down.
In regard to an article filling operation which should be performed in periodic basis, assuming now a situation in which the xe2x80x9cnon-fillingxe2x80x9d of articles occurs only once, the feeding of the packing material is shifted from a reduced velocity state to a normal velocity state within a unit packing period, resulting in inevitable sudden acceleration for feeding the packing material. Such sudden acceleration may cause instability in feeding the packing material. The instable feeding would result in a difference between the length of fed packing material required to produce one bag and the length of actually fed packing material, leading to a degraded quality of resulting bags and the production of defective bags.
It is therefore an object of the present invention to provide a packing material feeding apparatus for a vertical-type bag form-fill-sealing machine which is capable of stably feeding a packing material, even in a situation where the xe2x80x9cnon-fillingxe2x80x9d of articles occurs, to accurately maintain the length of produced bags at a required length.
The above object is achieved by the present invention which provides a packing material feeding apparatus for a bag form-fill-sealing apparatus, which comprises a feeding device for feeding a packing material; and a controller for controlling a packing material feeding velocity through the feeding device, the controller including a deceleration state for decelerating the packing material feeding velocity from a constant velocity when articles are not filled during a normal operation of the bag form-fill-sealing apparatus; and an acceleration state for increasing the packing material feeding velocity to the constant velocity when filling of the articles is resumed after starting the deceleration state, wherein the acceleration state is executed using a period equal to or longer than the unit packing period.
According to the feeding apparatus described above, since the acceleration state of the packing material is executed over a unit packing period or longer, the acceleration is smoothly performed. For this reason, the length of the fed packing material is accurately controlled, so that the length dimension of individual produced bags can be maintained at a predefined length to stabilize the quality of the bags.
The deceleration state may include a deceleration interruption mode for temporarily interrupting the deceleration of the packing material to maintain the packing material feeding velocity at a uniform velocity.
Likewise, the acceleration state may include an acceleration interruption mode for temporarily interrupting the acceleration of the packing material, and maintaining the packing material feeding velocity at a uniform velocity.
More specifically, the deceleration state further includes a first and a second deceleration mode executed before and after the deceleration interruption mode, while the acceleration state further includes a first and a second deceleration mode executed before and after the acceleration interruption mode.
In this case, since the feeding of the packing material is gradually decelerated in the deceleration state, the packing material is slowly stopped. Likewise, in the acceleration state, since the feeding of the packing material is gradually accelerated, stable acceleration of the packing material is achieved. As a result, the length of the fed packing material can be accurately controlled even in the deceleration state and the acceleration state.
Preferably, the packing material feeding velocity is set equal in the deceleration interruption mode and in the acceleration interruption mode. In this event, if the packing material is being fed in the deceleration state, i.e., in the deceleration interruption mode, due to xe2x80x9cno-fillingxe2x80x9d of articles, the feeding of the packing material can smoothly proceed from the deceleration interruption mode to the acceleration interruption mode of the acceleration state, provided that the filling of the articles is resumed within the next unit packing period.
Such direct transition of the packing material feeding from the deceleration interruption mode to the acceleration interruption mode does not involve stopping the feeding of the packing material, so that the machine can provide a continuous operation, thus reducing the frequency of operations shut-down.
Further, the controller preferably matches the total length of the fed packing material in the deceleration state and the acceleration state with a length required to produce one bag.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirits and scope of the invention will become apparent to those skilled in the art from this detailed description.